The invention relates to the reading of information which is contained in radiation emitted by information storage media.
A luminescent foil or plate can be provided with latent information, e.g., an image, which is releasable in the form of radiation when the foil is stimulated or excited. Phosphor foils, which constitute one type of luminescent foil, are being substituted with increasing frequency for conventional x-ray film in medical diagnostics. As compared to conventional x-ray film, phosphor foils have the advantage of almost linear reproduction characteristics. The image quality is therefore much less susceptible to an overly large or excessively small dose during the production of an x-ray image. Phosphor foils also have the advantage that they can be reused. Thus, once an x-ray picture has been made and the recorded information read and stored in an electronic device, a phosphor foil can be erased and used for additional x-ray images. A further advantage of phosphor foils is that their mechanical handling characteristics are largely the same as those of conventional x-ray film. For the most part, existing loading and unloading apparatus for x-ray film handling devices, such as x-ray film cassettes, can accordingly be used for phosphor foils as well.
The German Patent Publication No. 37 31 203 A1 discloses a method and apparatus for handling phosphor foils. Here, a phosphor foil is first loaded in an x-ray film cassette. Data relevant for an x-ray exposure to be made on the foil are then entered in a semiconductor memory on the cassette at an identification station. These data include patient name, birth date, treating physician, etc. An x-ray exposure is subsequently made. To read the x-ray image, the cassette is inserted in a digital reading apparatus. The cassette is opened, and the phosphor foil is removed and excited by a scanning device. The phosphor foil emits light which is taken up by a light collecting device and converted into a grid of digital signals. These signals can be processed in a digital image processing unit.
When a phosphor foil is scanned to recover information, one of the considerations is to detect as much of the emitted radiation as possible. As a rule, the foil is excited by a laser beam which causes the stored x-ray energy to be released in the form of low-energy radiation, advantageously in the form of visible light having a predetermined wavelength.
The German Patent Publication No. 29 51 501 teaches a device for reading information in radiation. The device takes up the radiation emitted by a luminescent foil or plate and conducts it to a radiation detector. This device has a drawback in that rays which travel almost perpendicular to the foil either do not penetrate the light conducting arrangement leading to the radiation detector or impinge upon the conducting arrangement at a very large angle. In the latter case, the rays are poorly coupled when the light conducting arrangement consists of optical fibers.